In re-establishing missing corners, where no bearing or witness tree or trees can be found, the land surveyor shall establish the missing corners in accordance with the government surveys. Where government surveys cannot be accurately followed, missing corners shall be established by proportionate measurement or existing landmarks supplemented with other location data, monuments, distances and the monuments for the corners shall be replaced according to the best calculations of the land surveyor, taking into account all the data, and, if necessary, replacing the proportionate measurement requirement.